[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [PATCH] tools/xenstore: don't store domU's mfn of ring page in xensotred
On 29/04/2020 11:49, Jürgen Groß wrote: > On 29.04.20 12:39, Igor Druzhinin wrote: >> On 29/04/2020 10:22, Julien Grall wrote: >>> Hi Juergen, >>> >>> On 29/04/2020 06:51, Jürgen Groß wrote: >>>> >>>> Recreating the event channel would be fine, but I don't see why it >>>> would ever be needed. And XS_INTRODUCE is called only at domain creation >>>> time today, so there is obviously no need for repeating this call. >>>> >>>> Maybe the idea was to do this after sending a XS_RESUME command, which >>>> isn't used anywhere in Xen and is another part of Xenstore which doesn't >>>> make any sense today. >>> >>> Commit f6cc37ea8ac71385b60507c034519f304da75f4c "tools/oxenstored: port >>> XS_INTRODUCE evtchn rebind function from cxenstored" added the exact same >>> behavior in the OCaml XenStored last year. >>> >>> This was introduced 12 years after C XenStored, so surely someone think >>> this is useful. We should check why this was introduced in OCaml XenStored >>> (I have CCed the author of the patch). >>> >>> If we still think this is not useful, then you should add an explanation in >>> the commit message why the two implementations diverge and possibly update >>> the spec. >> >> Thanks for CC, Julien. >> >> We indeed already use this functionality in our toolstack for guest kdump >> functions. It's not possible in XAPI to adopt libxl model where almost >> everything >> is restarted for a domain entering kdump, so we have to use this message to >> rebind xenstore evtchn after soft reset without shutting down backends and >> recreating the whole subtree (frontends reconnect fine after that). >> >> We obviously only require it for now to be present in oxenstored only. >> Please don't remove this functionality if possible. > > If I read handling in libxl correctly, in the soft reset case XS_RELEASE > is issued before doing another XS_INTRODUCE. XS_RELEASE will result in > xenstored throwing away its related struct domain, so XS_INTRODUCE will > be possible again. >From what I remember it was not possible to keep xenstored data for a domain and at the same time perform release-introduce cycle (at least in oxenstored). It also involved firing @releaseDomain which caused havoc in other part of the toolstack. Igor
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